Resinous coating compositions based on poly(amide)imide form flexible and durable films and are particularly useful as wire enamels, varnishes, adhesives for laminates, paints and the like. Such poly(amide)imide base coating compositions are particularly noted for their long term high temperature capability of the order of 220° C., which, in addition to their other qualities, makes them particularly useful in electrical insulating applications such as for magnet wire enamels. This is as compared to the usual polyester and polyesterimide base coating compositions which do not have such highly continuous heat resistance.
Poly(amide)imides are generally prepared using relatively expensive organic solvents, the economic use of amideimide coatings has been inhibited. Therefore, it has been customary to use such poly(amide)imide compositions as overcoats over less expensive polyester or polyesterimide base coats.
Polyethylene terephthalate (PET) films are widely used as electrical insulating films in view of their mechanical and electrical properties, and relatively low production costs. However, PET films possess low thermal resistance and therefore are ranked as Class B insulation or lower. Polyaramid films, such as those commercially available from Du Pont under the trademark NOMEX, exhibit superior thermal resistance as compared to PET films but have reported dielectric breakdown problems.
Poly(amide)imide films exhibit mechanical properties, thermal properties, abrasion resistance, and chemical resistance that make them suitable as electrical insulation materials. While poly(amide)imide films exhibit a number of superior physical properties as compared to polyaramid and polyester films, cost and free standing film property considerations have hindered commercialization of poly(amide)imide films for electrical insulation applications.
What is therefore needed in the art is a cost-effective electrical insulation material that exhibits a suitable combination of mechanical properties, thermal properties, abrasion resistance, and chemical resistance.